Mental Illness and Violence: A Link?

Feb. 2, 2009 -- When horrific acts of violence erupt, such as killing rampages on school campuses or mass slayings by heads of families, the public often reacts by saying the offender must have been "crazy."

Although mental illness and violence are often thought by society to go together, the perception is not entirely true, according to a new study.

"Mental illness alone does not increase the risk of violence," says Eric Elbogen, PhD, assistant professor of psychiatry at the University of North Carolina at Chapel Hill School of Medicine, citing the results of his recent study published in the Archives of General Psychiatry.

But when mental illness is combined with other risk factors such as substance abuse, it does increase the risk of violence, Elbogen found. Mental illness "makes a difference but only in the presence of other risk factors," he says. Besides substance abuse, Elbogen looked at such other factors such as a history of violence, age, gender, and stressors such as losing a job or getting a divorce.

Mental Illness & Violence: The Study

Previous research has produced mixed results about the link between mental illness and violence, with some finding a clear association and other studies finding, as did Elbogen's, that alcohol and drug abuse increases the risk in the presence of a mental illness.

For his study, Elbogen evaluated data on nearly 35,000 people, all interviewed about their mental health, history of violence, and use of substances between 2001 and 2003. Participants were part of the National Epidemiological Survey on Alcohol and Related Conditions, conducted by the National Institute on Alcohol Abuse and Alcoholism.

The percentage of participants reporting a mental illness reflects the percentages found in the general population and in other studies, Elbogen says.

In a second interview conducted in 2004 or 2005, participants were asked about any violent behavior, such as committing a sexual assault, fighting, or setting fires, in the time between interviews.

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Mental Illness & Violence: Results

In all, 2.9% of participants said they had been violent in the time between the first and second interviews.

When Elbogen evaluated the possible associations between mental illness, violence, and other factors, having a mental illness alone did not predict violence, but having a mental illness and a substance abuse problem did increase the risk of violence.

The risk was increased even more if the person had mental illness, substance abuse problems, and a history of violence.

For instance, when Elbogen looked at those who only had a severe mental illness, 2.4% had been violent. But when he looked at those with major depression and substance abuse or dependence, 6.47% had been violent.

When he looked at those with schizophrenia, 5.15% reported violent behavior in the time period between the interviews. But when a person with schizophrenia also had substance abuse or dependence problems, 12.66% reported violent behavior in the time between the interviews.

The highest risk for violence was found in those who had mental illness, a substance abuse problem, and a history of violence. These participants had 10 times the risk of violence than those who only had mental illness.

Other factors that predicted violent behavior included a history of juvenile detention or physical abuse, having seen parental fighting, a recent divorce, unemployment, or being victimized themselves. Being younger, male, and low-income also boosted the chance of violence.

"There is a relationship [between mental illness and violence] but it's much weaker than most people think," he tells WebMD.

"I think a lot of people think mental illness is the usual cause if not the foremost cause of violence," Elbogen says, citing a survey in which 75% of respondents said they considered people with mental illness as dangerous.

But his study concludes that “the findings say mental illness is relevant and you can see that throughout the data. But it's not really one of the foremost causes of violent behavior [by itself] in our society."

Mental Illness & Violence: Second Opinions

Experts who reviewed the paper for WebMD say they hope the new research may change mistaken perceptions toward those who are mentally ill.

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"Having a severe mental illness alone doesn't predict anything," as far as violence, says Philip Muskin, MD, professor of clinical psychiatry at Columbia University in New York. The new results, he says, confirm some other studies with similar results.

For those affected by the severe mental illnesses evaluated in the study, Muskin says, "You are no more at risk for committing a violent act than anyone in the population."

Paul Appelbaum, MD, former president of the American Psychiatric Association and a professor of psychiatry at Columbia University, says, "If you take the body of data as a whole, I think what everyone would agree with is, if there is an impact of mental illness on violent behavior it is not very great. And there is no question that the overall contribution of people with serious mental illness to violence in our society as a whole is quite small."